Abstract
AbstractMethane hydrate close to the hydrate stability limit in seafloor sediment could represent an important source of methane to the oceans and atmosphere as the oceans warm. We investigate the extent to which patterns of past and future ocean‐temperature fluctuations influence hydrate stability in a region offshore West Svalbard where active gas venting has been observed. We model the transient behavior of the gas hydrate stability zone at 400–500 m water depth (mwd) in response to past temperature changes inferred from historical measurements and proxy data and we model future changes predicted by seven climate models and two climate‐forcing scenarios (Representative Concentration Pathways RCPs 2.6 and 8.5). We show that over the past 2000 year, a combination of annual and decadal temperature fluctuations could have triggered multiple hydrate‐sourced methane emissions from seabed shallower than 400 mwd during episodes when the multidecadal average temperature was similar to that over the last century (∼2.6°C). These temperature fluctuations can explain current methane emissions at 400 mwd, but decades to centuries of ocean warming are required to generate emissions in water deeper than 420 m. In the venting area, future methane emissions are relatively insensitive to the choice of climate model and RCP scenario until 2050 year, but are more sensitive to the RCP scenario after 2050 year. By 2100 CE, we estimate an ocean uptake of 97–1050 TgC from marine Arctic hydrate‐sourced methane emissions, which is 0.06–0.67% of the ocean uptake from anthropogenic CO2 emissions for the period 1750–2011.
Highlights
Methane hydrate in marine sediments may contain ;500–2500 Gt [e.g., Pin~ero et al, 2013] of carbon, of which ;100–600 Gt may be stored in the Arctic [Archer et al, 2009]
We focus on water depths of 400–500 m, which is the depth range of potential gas hydrate dissociation [Giustiniani et al, 2013; Marın-Moreno et al, 2013] during the 21st century
To illustrate the potential significance of Arctic hydrate dissociation, we have extrapolated our 21st century hydrate-sourced methane emissions over the entire Eurasian Margin (738N–858N; 08W–1608W, going eastward). These extrapolations have many limitations: current ocean temperatures are colder further east; ocean temperature changes are likely to vary along the margin; more gentle margin slopes in shallow waters may result in a larger potential area of gas hydrate dissociation; and porosity, permeability, thermal conductivity, hydrate saturation and distribution, and heat flow [e.g., Crane et al, 1991] in the sediments are likely to be heterogeneous along the margin
Summary
Methane hydrate in marine sediments may contain ;500–2500 Gt [e.g., Pin~ero et al, 2013] of carbon, of which ;100–600 Gt may be stored in the Arctic [Archer et al, 2009]. Based on the ages of carbonate samples from the 350 to 400 mwd venting area and their isotopic composition, Berndt et al [2014] showed that methane seepage has been active there for more than 500 year From their modeling of the response of the subseabed temperature field to seabed temperature variations that were measured continuously over a period of nearly 2 years, Berndt et al [2014] suggested that the observed present-day emissions may be controlled by seasonal changes in temperature. We assess the influence of decadal and seasonal fluctuations on the past and future response of marine hydrate-bearing sediments offshore west Svalbard, and constrain the associated future Arctic methane emissions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
